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Chlamydial and Other Infections

By J. Allen McCutchan, MD, MSc, University of California at San Diego

Chlamydial infections include sexually transmitted diseases of the urethra, cervix, and rectum that are caused by the bacteria Chlamydia trachomatis. These bacteria can also infect the eyes. Less commonly, other bacteria, such as Ureaplasma and mycoplasmas, cause infections of the urethra.

  • Symptoms include a discharge from the penis or vagina and painful or more frequent urination.

  • If unnoticed or untreated in women, these infections can result in infertility, miscarriage, and an increased risk of a mislocated pregnancy.

  • DNA tests of a sample of the discharge or of urine can detect chlamydial infection.

  • Antibiotics can cure the infection, and sex partners should be treated at the same time.

Several bacteria can cause diseases that resemble gonorrhea. These bacteria include Chlamydia trachomatis, Ureaplasma, and several types of mycoplasmas (a type of bacteria that lack a cell wall). Laboratories can identify chlamydiae but have difficulty identifying the other bacteria.

Chlamydial infection is the most commonly reported sexually transmitted disease (STD). In the United States, over 1.4 million cases were reported in 2012. Because the infection frequently causes no symptoms, twice as many people may be infected.

In men, chlamydiae cause about half of the urethral infections not caused by gonorrhea. Most of the remaining urethral infections in men are probably caused by Ureaplasma urealyticum or mycoplasmas. In women, chlamydiae account for virtually all of the cervical infections (cervicitis) that produce pus and that are not caused by gonorrhea. Sometimes both sexes have gonorrhea and chlamydial infection at the same time.

Chlamydial infection can also be spread during oral sex, causing infection of the throat.


In men, symptoms of chlamydial urethritis start 7 to 28 days after the infection is acquired during intercourse. Typically, men feel a mild burning sensation in their urethra during urination and may have a clear or cloudy discharge from the penis. The discharge is usually less thick than the discharge in gonorrhea. The discharge may be small, and symptoms mild. However, early in the morning, the opening of the penis is often red and stuck together with dried secretions. Occasionally, the infection begins more dramatically—with a frequent urge to urinate, painful urination, and a discharge of pus from the urethra.

Many women with chlamydial cervicitis have few or no symptoms. But some have frequent urges to urinate, painful urination, and secretions of yellow mucus and pus from the vagina. Sexual intercourse may be painful.

Chlamydial throat infection usually causes no symptoms.


If the infection spreads up women’s reproductive tract, it may infect the tubes that connect the ovaries to the uterus (fallopian tubes). This infection, called salpingitis, causes severe lower abdominal pain. In some women, the infection spreads to the lining of the pelvis and abdominal cavity (peritoneum), causing peritonitis. Peritonitis causes more severe pain in the lower abdomen. These infections are considered pelvic inflammatory disease (see Pelvic Inflammatory Disease (PID)). Sometimes infection concentrates in the area around the liver, in the upper right part of the abdomen, causing pain, fever, and vomiting—called the Fitz-Hugh-Curtis syndrome.

If the anus is infected, people may have rectal pain or tenderness and a yellow discharge of pus and mucus from the rectum.

Chlamydiae may be transferred to the eye, causing infection of the clear membrane that covers the white of the eye (conjunctivitis).

Chlamydial genital infections occasionally cause a joint inflammation called reactive arthritis (previously called Reiter syndrome—see Reactive Arthritis). Reactive arthritis typically affects only one or a few joints at once. The knees and other leg joints are affected most often. The inflammation seems to be an immune reaction to the genital infection rather than spread of the infection to the joints. Symptoms typically begin 1 to 3 weeks after the initial chlamydial infection.

If chlamydial urethritis is not treated, symptoms usually disappear in about a year. However, if untreated, a chlamydial infection can cause complications, especially in women who have been infected a long time. Complications include chronic abdominal pain and scarring of the fallopian tubes. The scarring can cause infertility and mislocated (ectopic) pregnancies (see Ectopic Pregnancy).

In men, chlamydial infections may cause epididymitis, which causes painful swelling of the scrotum on one or both sides (see Epididymitis and Epididymo-orchitis). Other bacteria from the intestine also contribute to these complications probably by infecting areas that have been damaged by chlamydiae.

Did You Know...

  • Chlamydial infections are the most common sexually transmitted disease.

  • Because chlamydial infection and gonorrhea often occur together, people with one of them are routinely treated for both.


  • Tests on a sample of discharge from the cervix or penis

Doctors suspect these infections based on symptoms, such as a discharge from the penis or cervix. In most cases, doctors diagnose chlamydial infections by doing tests that detect the bacteria’s unique genetic material (DNA). Usually, a sample of the discharge from the penis or cervix is used. For some types of these tests, a urine sample can be used. Thus, people can avoid the discomfort of having a swab inserted into the penis or having a pelvic examination to obtain a sample.

Gonorrhea, which is often also present, can be diagnosed using the same sample. Blood tests to check for HIV infection and syphilis are usually also done.

Specific tests for genital infections with Ureaplasma and mycoplasmas are not usually done. These infections are sometimes diagnosed in people with characteristic symptoms after gonorrhea and chlamydial infections are ruled out.


Because chlamydial infection is so common and because many infected women have no symptoms, tests to screen for chlamydial infection and other STDs are recommended for certain sexually active women and men.

Women who are not pregnant are screened if they have characteristics that increase their risk of infection:

  • Age 25 or younger

  • A previous STD

  • Participation in risky sexual activities (such as having many sex partners, not using condoms regularly, or participating in sex work)

  • A partner who participates in risky sexual activities

Pregnant women are screened at their first prenatal visit and, if they have risk factors for infection, again during the 3rd trimester.

Heterosexual men are not routinely screened except in settings with a high prevalence of chlamydial infection—for example, at an adolescent or STD clinic or when they are admitted into a correctional facility.

Men who have sex with men are screened only if they have been sexually active within the last year.


  • An antibiotic

  • Simultaneous treatment of sex partners

Chlamydial, ureaplasmal, and mycoplasmal infections are treated with a single dose of the antibiotic azithromycin taken by mouth or with doxycycline or levofloxacin taken by mouth for 7 days. At the same time, an antibiotic such as ceftriaxone, injected into a muscle, is given to treat gonorrhea because the symptoms of the two infections are similar and because many people have both infections at the same time. Pregnant women are given azithromycin instead of tetracycline or doxycycline, which must be avoided during pregnancy.

If symptoms persist or return, treatment is repeated for a longer period.

Infected people should abstain from sexual intercourse until they have completed treatment to avoid infecting their sex partners. Sex partners should be treated simultaneously if possible and should abstain from sexual intercourse until they complete treatment.

The risk of another chlamydial infection or another STD within 3 to 4 months is high enough that people should be tested again at that time.

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